This invention relates to the treatment of waste material from silviculture and like operations. It is conventional to draw a distinction in such treatment between chipping and shredding.
Generally speaking a chipper comprises a series radially extending blades mounted on a fly-wheel, and brushwood is fed in a direction generally normal to the plane of the rotating fly-wheel and cut into a series of discrete pieces. Because of the fibrous nature of the wood, larger diameter branches tend to split into a number of chips per cut, but smaller branches form a single chip from each cut.
However, chippers have limitations. Particularly thin and pliant material may not shear satisfactorily. Material with a substantial foreign body content is also unsuitable to be chipped. For example, if a sapling is up-rooted and chipped, and if the roots carry soil and stones, the stones may damage the cutter blades. As a generalisation it may be said that material which is either too soft or too hard is unsuitable for chipping.
Moreover, there is a requirement for material to be shredded finely so as to be compostable and hence recycled into the soil more quickly than is possible with mere chipped wood. This possibility is applicable even to material which is capable of being chipped satisfactorily.
Existing shredder machines commonly operate on a flail principle. That is to say, individual flail cutters are freely pivoted to a drive shaft which requires to be rotated at a substantial speed to cause the cutters to fly out centrifugally to the operating position and the waste material is then fed into their path. As a consequence of the speed and mass, the power requirement is high and frequently the noise level from an operating shredder is also high.